The present invention relates to a sheet processing apparatus. More specifically, it relates to a sheet processing apparatus which can be mounted on the side of an image forming apparatus and which performs processes such as stamping on sheets discharged from the image forming apparatus.
For example, a copying machine may have a mechanisms for performing a stamping process and for punching holes in copy-processed sheets. In such a copying machine, the stamping mechanism and the punching mechanism are disposed downstream of a fixing unit. The stamping mechanism will include stamps, or a stamp unit comprising, for example, a thermal head or an ink ribbon, as a stamping member, as well as a mechanism for pressing either onto a sheet. Where sheet-stamping is performed, transportation of the image-fixed sheet is halted and the stamp or the stamp unit is pressed onto the sheet. Wherein holes are punched in a sheet, it the sheet is transported to a predetermined position, and then held so as to be punched by the punching mechanism.
It the copying machine equipped with the stamping mechanism, stamping can be performed along the leading or the trailing margin of a sheet by accordingly regulating the transportation of the sheet. More specifically, the stamp position is variable in the sheet transport direction. However, wherein stamps are employed for performing stamping operations, the stamp position cannot be varied in the width direction of the sheet. On the other hand, wherein the stamp unit containing a thermal head is used, the stamping position can be made variable in the sheet width direction by providing a head which extends accordingly and controlling each element thereof. Such an apparatus, however, is expensive and its control is complicated.
Still further, since this conventional sheet processing apparatus is provided between the fixing unit and discharge rollers within the body of a copying machine, it is impractical to fit the stamping mechanism to a copying machine not previously equipped with a stamping function.
In a copying machine equipped with the foregoing stamping and punching mechanisms, the distance from the fixing unit to the discharge rollers is increased, due to the location of the mechanisms in line along the transport path of the sheet. The machine thus outfitted is made bulkier, and additional time is required to discharge a sheet, even wherein the stamping and punching processes are not carried out.
In one means of disposing the stamping and punching mechanisms in a reduced space, the leading edge of a copy sheet is fed into a latter-stage unit, for example a sorter, during the operations performed by each mechanism. In this case, further process control in the operation of the latter-stage unit during the functioning of each mechanism becomes necessary.
Furthermore, since the stamping and punching mechanisms operate at different timings, extra time is spent in performing these processes.